System of photographic reproduction



Nov. 3, 1959 A. BARIL, JR., ETAL 2,911,299

SYSTEM OF PHOTOGRAPHIC REPRODUCTION za im l 6 w rfb ,M C; H ,H

f ffy/a ifa Nov. 3, 1959 Filed July 22, 1952 fff lll/OHRA 7 E iff/$762 EA. BARIL, JR., ErAL SYSTEM oF PHOTOGRAPHIC REPRODUCTION 3 Shececs-SheetI3 www@ /PEZXED [4579/62 E @@ll @@@lll OOOOO OOOOO United States Patent OSYSTEM F PHOTOGRAPHIC REPRODUCTION Albert Baril, Jr., Irvin H. DeBarbieris, and Robert T.

Nieset, New Orleans, La., and Thornton Stearns, Winchester, Mass.,assignors, by mesne assignments, to Kalva'r Corporation, New Orleans,La., a corporation of Louisiana Application July 22, 1952, Serial No.300,282

1 Claim. (Cl. 96-49) The present invention relates to a process offorming copies of records such as printed matter or microlms by means ofcompounds which produce gas upon irradiation, and also to materialwherein such copies can be formed, and to the copies themselves.

It is a principal object of the invention to provide photographicreproductions according to a technique which is extremely simple andinexpensive and yet fully satisfactory particularly for use in oiiices,libraries, drafting rooms and similar establishments where it isdesirable to copy record material with a minimum of effort, withunskilled labor, and in minimum time.

Another object is to provide such a technique which employs materialthat is comparatively inexpensive, stands up well through reasonablyrough routine handling, and produces exact and permanent copies.

Further objects are to provide a reproduction technique which is drythroughout and does not require chemical treatment or rinsing baths, andto provide such a technique which optionally permits the direct printingof either negative or positive copies, -with the same material,apparatus, and general procedure.

In accordance with the invention, an essentially stable photographicrecord is produced in a vehicle of adjust- :able rigidity containing asensitizing substance capable of liberating -gas upon exposure toradiation, in the form of gas sources or units that are essentiallyinvisible upon generation and while the vehicle remains indurated but'which are capable of expanding into visible bubbles With- ;'in therelaxed vehicle, by exposing a layer of the vehicle,

in either indurated or relaxed condition to a radiation :image thusforming therein a record in terms of gas'units, fby relaxing orindurating, respectively, the vehicle to bring fit into the othercondition with image selected units exjpanding into bubbles to form anal visible record, and vby rendering ineiective the sensitizer whichmight remain `Within the vehicle in portions which are not occupied by'-,the bubbles which form the final record, thus xing the :recordagainst further exposure; in an important embodiment the xed 4vehicle isin irreversibly hardened indurated condition.

In a practically important aspect of the invention, a Elayer of thevehicle is exposedin indurated condition to iform therein a record interms of gas units, the vehicle lis then relaxed to form a record interms of bubbles, and.

the sensitizer which after exposure remains within the vehicle isrendered ineffective and the copy fixed by Auniformly exposing it and bydiffusing the gas units thus iformed from the indurated vehicle, orfixation is accomgas units, the gas is then permitted substantially todiuse from the vehicle, an overall exposure is applied to gen- Verategas sources from the remaining sensitizer, the vehicle relaxed to expandthe gas units resulting `from the Ffice 2 Y overall exposure to form arecord in terms of bubblesgand a fixation step vis applied. v -v ln anadditional aspect, `a layer of the vehicle is exposed in induratedcondition yto form a record'in terms of gas units, the gas is dilusedfrom the vehicle, the vehicle is relaxed, and an essentially uniformexposure is applied to generate gas units from the remaining sensitizerwhich units expand into record dening bubbles; fixation follows.

ln a further aspect, a layer of the vehicle is exposedv in relaxedcondition to form a record in terms of gas bubbles, the vehicle is thensuiciently indurated essentially to prohibit further bubble formationwhile permitting diffusion of gas, a substantially uniform overallexposure is applied to generate gas from the remaining sensitizer, andthe remaining gas is permitted to diffuse.

Reproduction material according to the invention comprises a layer ofvehicle material of adjustable rigidity and permeability incorporatingan amount of sensitizing substance .capable of generating sufficient gasto form a visible record in terms of gas bubbles upon exposure toradiation and expansion of the gas, the vehicle being characterized by arigidity which is adjustable between optimal degrees, one of higherrigidity preventing substantial bubble formation but of sutlcientpermeability to permit gas unit formation and if desired gas diffusionfrom the vehicle, and the other of lower rigidity permitting gas bubbleformation with permeability permitting escape of gas from the vehicle.In an important embodiment the vehicle is of the gelatin type,suiciently indurated at ordinary temperatures to prohibit bubbleformation, suciently relaxed at moderately elevated temperature topermit bubble formation, and becoming irreversibly hardened to a highlyindurated condition upon heating to a further ele-v vated temperature.

Final copies according to the invention comprise an in durated layer ofplastic material of essentially uniform thickness which contains insubstantially uniform distribution chemically unchanged photolyticdecomposition products of a radiation sensitive substance, andessentially bubble shaped cavities distributed in a record V formingpattern, the configuration of the individual bubbles as well as theirdistribution being fixed by therigidity ofthe indurated vehicle. In animportant embodimentA the vehicle consists of irreversibly hardenedgelatin.

Other objects, aspects and features will appear, in ad- Figs. 7 and 8are diagrams illustrating the rigidityad justrnent according to theinvention; and f Figs. 9 to 12 are diagrams illustrating four respectiveembodiments of the process according to the invention.

The following description presents first the general operationalprinciples of the most important aspects ofl the invention with regardto the properties of vehicle and sensitizing substance, and thensupplies speciic examples of materials as well as of process sequenceswhich incorporate these principles for various practical purposes.

'I'he photographic reproduction system according to the invention isbased on the possibility of determining a record pattern in terms oftransmission, absorption, re-

flection and scattering 'of the incident light by the con-l trolledformation of a structure of gas bubblesV within a vehicle, coated onsuit-able sheet stock or Self-supporting.

The primary photochemical, reaction releases gas in a pattern determinedby a radiation image, in proportion to the amount of radiant energyabsorbed by a sensitizing substance.

The term record as herein .used denotes `any picture. or indiciapatternl in terms of eectively tangible characteristics of a body, suchas texture or grain distribution., A record should be distinguished froma radiation image as dened by a beam that is modulated by an originalrecord, in direct contact with the copying surface or related theretothrough the intermediary of an image forming system. The term originalis used for any object that modulates the radiation to which thesensitive substance is exposed; it can be a scene, anV original pictureor print, or a photographically or otherwise produced positivev ornegative copy. The term radiation as herein used includeselectromagnetic radiation suchl as light Vwithin and on either side ofthe visible spectrum, as well as particle impingement.

The material which is used in the present system has two essentialcomponents in intimate cooperation, namely the vehicle and thesensitizing substance. A vehicle is the carrier or binder material forsensitizing substances and for the gas released therefrom uponphotolysis, which gas occurs in the form of initial sources or units,and as record forming bubbles. A sensitzing substance or sensitizer forshort, is radiation sensitive material incorporated in the vehicle whichgenerates gas by decomposition upon irradiation.

The vehicle must have two properties in order to be usable for purposesof the invention, namely, permeability and adjustable rigidity.

The permeability has two important aspects, namely, the internalpermeability or rate of diffusion of gas within the vehicle itself andthe escape permeability, that is the rate at which gas can escapeentirely from the vehicle.

The rate of diffusion of the gas within the vehicle itself (internalpermeability) varies between an upper and lower limit. TheV lower limitof diffusion is determined by the need for gas to move with suflicientfreedom to obey Boyles and Charles laws. relating the volume to pressureand temperature, respectively, after the release of what is hereinreferred to as gas sources, from the irradiated sensitizing substance.These sources can. be conceived as single gas molecules or groupsthereof, but at any rate they do not yet form units of a true. gas. Ifthese sources were trapped within the vehicle upon release byphotolysis, they could not form the smallest units with the abovecharacteristics of a true. gas, which units might also be referred to aslatent bubbles or bubble nuclei. These sources and units constitute aninvisible latent record of the image defining radiation pattern whichcauses their release from the sens'itizer within the vehicle. The gascontents of the unitsl or latent, bubbles varies to a degree which canbe controlled by way of the internal permeability. The upper limit ofinternal permeability is determined by the spatial resolution requiredin the finished product, and hence by the size of the ultimate recordforming bubbles. For example a microfilm print intended for projectionuse requires but a very small bubble. On the other hand' reproductionfor example of large size prints by contact exposure permitsconsiderably larger bubbles. For a resolution of one thousand lines perinch, bubbles of approximately 2 microns are needed, and such a bubblewould contain approximately 2x10-13 moles of gas. Accordingly, forapplications requiring resolution of this fineness, the diffusion of thegas and hence the interna permeability of the vehicle has to be soadjusted that units containing substantially more than this amount ofgas'do not occur. Furthermore, the internal permeabllity has to be soregulated that the gas does not diffuse away from the exposed' areasinto unexposed areas Where 1t might later cause general backgroundfoggn.

This property of the vehicle, providing for optimal internal diffusionof the gas, is illustrated in Fig. l where dots m represent molecules ofthe sensitizer which is dispersed in the vehicle v. In Fig. 2 crosseddots s represent sources of gas, generatedrbyV irradiation with aradiation image pattern z'. At this stage the molecules released inphotolysis cannot truly behave as a gas and, therefore, no bubble recordcan be formed if internal diffusion is so restricted that the partialvolumes are small, containing only one or Very few gas molecules.

The operative situation is represented in Fig. 3. Here the partialvolumes are sufficiently large so that great numbers of the gasmolecules can act together, behaving in units zz asV an ideal gas, andforming under high pressure the latent bubble agglomerates indicated ascrosses which can expand to a maximum size determined by the rigidity ofthe vehicle, as will be discussed below. Fig. 3 also indicates how therecord detail can be obscured or even expanded into the unexposedbackground, thus creating a fogged area, if diffusion 'is very great andmarginal units um form beyond the actually exposed area.

While, as above discussed, the vehicle` should be of suflicient internalpermeability to allow the optimum diffusion of gas once formedtherewithin, it should have a reasonably impervious surface so that gasis not completely lost from the emulsion during exposure, therebyreducing the cfiiciency and hence the sensitivity of the emulsion or thefilm. Efficiency is here defined as the ratio of the actual volume ofgas confined in light scattering bubbles, to the amount released atstandard conditions of pressure and temperature. This efiiciency isaffected by the above loss of gas and by the flow characteristics of thevehicle to be discussed below. Low efiiciency means low sensitivitybecause it requires more energy to activate sufiicient sensitivematerial to give a required contrast. The loss in sensitivity due to lowefficiency cannot be compensated for by increased concentration ofsensitizer because, if the concentration exceeds a certain rathercritical value, then the gas units are initially too large and impairthe resolution. A high efficiency therefore enhances sensitivity as wellas detail resolution. The efficiency is also affected by the duration ofthose periods of the record forming technique during which the vehiclepermits escape of gas.

The escape permeability of the vehicle furthermore aects the permanenceof the final record which will be further discussed below. If afterrecord formation the permeability of the vehicle is so changed that anyfur` ther gas released by photolysis can escape quickly without formingbubbles, then the record is xed against subsequent exposure. Thus, whileit is in the interests of efficiency desirable to have a low rate of gasescape prior to record formation, it is desirable to have a high rate ofgas escape thereafter. However, fixation is promoted by this gas escapeonly if the gas previously Iconfined in the bubbles is no longerrequired to preserve the bubble structure. This, in turn, depends uponthe rigidity characteristics of the vehicle which will now be discussed.

The rigidity characteristics of the vehicle have to conform to certainrequirements during the principal steps of the present technique,namely, exposure, development, and fixation.

During exposure for the purpose of providing a latent record thevehicle, in addition to the above discussed internal permeabilitypermitting formation of gas units, must have suflicient rigidity orresistance to fiow to prevent the formation of expanded units or bubblesduring exposure. Such bubbles would scatter light in the highlightedareas, thus cutting ofi further photolysis in these regions, causinginsufficient exposure and reducing coutrast. 'These considerations applyto exposure leading to formation of bubbles which constitute a finalrecord, while. they do not apply for purposes of preliminary,

5. although pattern determining, exposure of a relaxed vehicle, as willbe pointed out below with reference to a practical example of this type,illustrated in Fig. 1l.

To convert or develop the record in terms of gas units or latent bubblesproduced during exposure, into a visible record, the vehicle is relaxedin such rfashion that the latent bubbles can expand to cross sectionswhich will produce the maximum light-scattering effect consistent withthe required resolution. Fig. 4 indicates this stage of bubbleformation. The circles b which surround units u represent bubbles ofdesirable relative proportions. Fig. 5 indicates the record structureupon diffusion of gas from now empty bubbles be. These diagrams do notindicate possibilities of removing the remaining sensitizer m, whichwill be discussed below. In a practical and satisfactory embodiment, theaverage diameter for good resolution is about 2 microns, bubbles above 5microns in diameter being undesirable. a

In accordance with the present invention, the ratio of the cross sectionof the gas unit formed during exposure can be controlled for purposes ofoptimal utilization of the photosensitive material during exposure, andof increasing the overall efficiency of the whole photographic process.This ratio is therefore `an amplification factor and will be so referredto herein.

Of equal importance to unit formation by internal diffusion is theincrease Iin overall quantum eiliciency that can be obtained byutilizing the ygas amplification principle. The pressure under which thegas is released during exposure is a function of the concentrationof thesensitive material, the primary quantum eiciency of decomposition of thephotosensitive material upon irradiation, and the rigidity of thevehicle Vagainst which the gas -must expand. In accordancewith theinvention these three variables are adjusted Yto limit the size duringexposure to negligible light-scattering cross sections. We found thatthe gas amplification factor increases the overall quantum eficiencybeyond that which can be obtained by coupling the decomposed materialwith a dye.

Fig. 6 indicates the undesirable condition where internal diffusion hasbeen too rapid kor relaxation gone too far so that large bubbles bl haveformed which obscure the detail.

Development by relaxing the vehicle accomplishes the above discussedamplification by purely physical means. If the vehicle -is athermoplastic, the requisite conditions of plastic ow during developmentcan be brought about by the amplification of heat by conduction,convection or radiation. The physical means for applying heat to obtainregulated relaxation and induration consistent with a large gasamplification factor can be quite simple, which is a primary advantageof the invention.

Fixation has the purpose of making the record stable and permanent ingeneral use. The record must not disappear or be reduced incontrast orsharpness subsequent to development by losingits light scatteringproperties, it must be stable against fogging or accidental re-exposure,and it must be mechanically stable, that is sufficiently hard towithstand ordinary handling, including damage by scratching or softeningunder the heat of a projector lamp.

Preservation of the record proper can be accomplished by hardening thevehicle after the bubbles have been alloWedtheir maximum expansionduring development. This freezing of the bubble structure brings aboutfixation by sealing up each individual bubble to confine the gastherewithin, and by making the walls of each bubble sufficiently rigidso that even though the gas subsequently escapes, the wall remains,forming a light scattering cellular structure which is mechanicallystrong enough to maintain itself against ordinary use. It is this secondaspect that is especially important since it preserves the recordregardless of gas diffusion from the vehicles. This nal hardening isespecially beneficial because irreversible and of a high degree, if thevehicle is of the gelatin`V type, as will be discussed more in detailbelow.

'Ihe vehicle can be stabilized against exposure and fogging bydestroying detrimental sensitizer, by permanent hardening, and byoptical screening.

The destruction of remaining lsensitizing material which was not neededfor `formation of the final record, can be accomplished in several ways,three of which have proved to be especially important for the processaccord ing to the invention.

The first Way is `to make the material thermally unstable such as toprevent it from producing gas. This technique is applicable -to thediazo sensitizer used in an important embodiment of the invention. Suchmaterial chemically decomposes at elevated temperatures, but in such away that the yield of gas from thermal decomposition is much lower thanit is for photodecomposition.

Another way of destroying the remaining sensitizer is the diffusion ofthe released gas such that, as rapidly as the gas is formed byphotodecomposition, it escapes completely from the vehicle so thatbubbles cannot form. Particularly effective is the combination ofoptical screening in the manner pointed out below and of slow diffusionof gas released thus destroying the remaining photosensitive materialsimply by exposure to a lower level of illumination than is required forinitial exposure.A

A third means of inactivating the remaining sensitizer is to eliminate avolatile component of the primary photochemical reaction'. In agelatinous vehicle for example,

this can be accomplished by way of driving olf the waterthat is requiredfor the eficient release of gas by photodecomposition. At temperaturespractical for relaxation development and iixation, most of the water isdriven off. In the absence of water, the quantum efficiency of thephotochemical reaction that remains possible is so much less than thequantum eliciency in the presence of water,v that the sensitivity isgreatly reduced. Y

Subsequent to the fixation process proper, the vehicle can be made toohard and resistant for bubbles to form readily under ordinary exposureconditions. Even though small amountsv of gas are released by subsequentexposure it cannot expand into bubbles of significantly light-scatteringcross section. This condition is essentially identical with thatlmentioned above as required for theprigid preservation of the cellularstructure, and it goes hand in hand with the mechanical stabilitymentioned below which is desirable as a protection against scratchingand other mechanical deformation in routine handling of the material. v

Stabilization of the sensitizer is aided by changing the spectraltransmission characteristics of the vehicle. The vehicle and sensitivematerial, before and during exposure, passes radiation of a criticalwavelength required for the primary photochemical reaction. Afterexposure however, the spectral transmission characteristics of thevehicle can in many instances be so changed that it becomes opaque tolight of the critical wavelength. This is in effect equivalent toWrapping up the unexposed parts of the lm in black paper forever after.In the case of gelatinous vehicles carrying certain diazo compounds assensitizers, for example, this can be accomplished concomitantly withthe nal hardening induration which in this instance somewhat tans thesurface of the gelatin. This tanning and some coagulation within theemulsion renders the gelatin'less transparent to the ultraviolet lightin the general region of 3600 A., so that the actinic spectral regionmainly effective for image formation is liltered out.

Mechanical stability is in the mainv provided by the indurating andhardening procedures described above. A

mechanical structure sufficiently rigid to preserve the l bubbles whichconstitute the record, as well as to prevent the direct expansion ofbubbles upon further exposure is sufficiently hard to meet all the usualphotographic` needs.

In order to perform the above-outlined functions within the frame workof the invention, the materials employed therein are compounded andselected as follows.

The sensitizing substance must be capable of dispersion within thevehicle suiciently line for purposes of the required definition asfurther controlled by the abovediscussed permeability and rigiditycharacteristics of the vehicle. Compounds of the diazo type which uponirradiation liberate nitrogen were found to be especially suitable, butother compounds for example of the type which liberate carbon oxides canbe used.

Among the sensitizing substances which liberate nitrogen units uponirradiation, para-diazo dimethyl aniline zinc chloride was found to beespecially valuable, but the following substances were also found to beusable.

P-diazo diphenylamine sulfate, p-diazo diethylaniline zinc chloride,p-diazo ethyl hydroxyethylaniline zinc chloride, p-diazo ethyl methylaniline zinc chloride, p-diazo diethyl methyl aniline zinc chloride,p-diazo ethyl hydroxyethylaniline Zinc chloride, l-diazo-2 oxynaphthalene-4r sul-fonate, p-diethyl amino benzene diazonium chlorideZnCl2, 4-benzoylamino-2-5-diethoxy benzene diazonium chloride,p-chlorobenzene-sulfonate of 4-diazo-lcyclohexylaniline,p-chlorobenzene-sulfonate of 4diazo2 methoxy-l-cyclo-hexylamino benzene,tin chloride double salt of 4-N-nethyl-cyclohexylamino-benzene diazoniumchloride, p-acetarnino benzene diazonium chloride, 4-dimethylarninobenzene diazonium chloride, S-methyl 4- diethyl amino benzene diazoniumchloride, 4-morpholino benzene diazonium chloride, 4-piperidyl2-5-diethoxy benzene diazonium chloride, l-dimethyl amino naphthalene-4diazoniurn chloride, 4-phenyl amino diazo benzene diazonium chloride. A

Substances which liberate carbon oxides upon irradiation and which areuseful for purposes of the invention are organic acids such as ferricammonium citrate and oxalic acid.

For incorporating sensitizers in vehicles used for purposes of theinvention, two techniques are feasible.

The sensitizing compound can be dissolved and in that state mixed with asolution of the plastic, and the mixture dried in the form of a filmapplied to a support. This technique is particularly applicable togelatinous vehicles. Up to certain concentration-s which depend on theparticular gelatin, such vehicles contain the sensitizer most likely inmolecular dispersion dissolved in the gelatin water. Above suchconcentrations the sensitizer is probably also dispersed in precipitatedform, as will be discussed below with reference to the vehiclestructure.

The sensitizing substance can also be incorporated in vehicles which aremade from organosols which can be kfused at temperatures below, althoughrather close to the decomposition temperature of the sensitizingsubstance, which condition must be taken into account in preparing suchmaterial.

The vehicle material plays a very important role within the framework ofthe present invention. It must lend itself easily to quick, positivelycontrollable and reversible transformation from relaxed or amplifyingcondition into indurated condition, and vice versa, and in an importantmodification also to irreversible transformation into highly' hardenedcondition. In either state, permeability is to be preserved, but iniinal irreversible induration or hardening the escape of gas can beexcluded if desired.

In accordance with the invention, this transformation is accomplished bythe purely physical expedients principally of temperature, and sometimesof moisture, or both. For most purposes dry heat is sufficient, with theensuing practical advantages. The vehicle is for practical purposes ofsuch a nature that it softens if the temperature is raised during thedevelopment process. As it softens, the gas units and bubbles areallowed to expand as above explained. After the bubbles have reachedtheir optimum diameter, another change in temperature leads again toinduration, either of the reversible, or at choice of the hardening orfinal type. This cycle can be carried out for certaingelatin emulsionssuch as herein described. As theV temperature is raised, gelatin ofselected types softens somewhere between and 200 F. allowing the bubblesto expand. As the temperature goes above 200 F., the gelatin tans on thesurface somewhere between 200 and 250 F., and, in general, assumes a.hard, rigid and irreversibly coagulated structure, which then providesthe above discussed mechanical rigidity which freezes the bubble wallsand preserves .the structure even though the gas may subsequentlyescape. Vehicles of the Bakelite type are somewhat similar. They becomeplastic at an inter-mediate temperature of about 200 F., the approximatetemperature required for expansion of the bubbles, and at a highertemperature of about 250 or 300 F., polymerize irreversibly.

Other vehicle characteristics can be utilized With slight modificationof procedure. For example, a completely ythermoplastic vehicle can beused which, when warmed to about 200 F. flows quitefreely, thusproviding the characteristics necessary for development by bubbleamplication. Such a material need not have thermo-setting properties ifit can be indurated by cooling it rather rapidly after development hastaken place. Such reversibly controllable materials can be re-exposedand re-developed by proper sequences of heat and light application, butcan 'oe rendered stable against the application of heat alone or lightalone as might be encountered in subsequent use. Still another type ofvehicle material can be cooled rapidly'enough after development toassume an irreversible structure or degree of hardness that rerquiresthe application of extremely high temperatures to plasticize it again,being in this respect somewhat analogous to the rst mentioned type.

For any'particular material, the optimum temperatures on either side ofthe transition points between relaxed and indurated conditions depend tosome extent upon the technique of printing. The vehicle has to be chosenwith regard to the relation between bubble gas pressure, rigidity,permeability, and to some extent also withregard to the recordcharacteristics required, which may vary according to emphasis on linegrain, density, or other properties.

Figs. 7 and 8 illustrate the above-described temperature determinedrigidity characteristics, which are a principal expedient within theprocess according to the invention.

Fig. 7 relates to vehicle material of the gelatin or bakelite type,which exhibits upon increase in temperature three distinct regions ofinduration. The low temperature range marked Arepresents an induratedyet permeable phase which is mainly employed during exposure of theareas of the final record. is relaxed permitting bubble expansion ordevelopment. In range C, the Ivehicle indurates permanently and to ahigher degree. This cycle is reversible so far as ranges A and B areconcerned but irreversible from range C.'

It will appear hereinbelow that the invention can be carried out withinthe reversible transformations between A and B, without reaching C,although use of the latter con-l stitutes an important aspect of theinvention.

In the case of gelatin vehicles, the function of range C is particularlyassured through the tanning and hardening of the surface layer ofgelatin, which acts somewhat as a barrier for the re-entrance orre-absorption of water. Such vehicles are as hard and stablemechanically as. ordinary photographic emulsion.

Fig. 8 illustrates another cycle which can be carried out with.thermoplastic vehicles which do not have a permanently indurated phase,but also with vehicles of the gelatin type if range C is not used.

Expedients other than heatcan be used alone or in cooperation with atemperature cycle.V Such an expedient is'moisture, especially forgelatinous vehicles. Another in range B the vehicle expedient istheabove mentioned optical fixation by way y of changing the lighttransmittingcharacteristic of the vehicle in range C. In the case ofgelatin the tanning effect which vaccompanies the hardening indurationcan be utilized for this purpose. Y

The internal structurel of the vehicle is as important a characteristicas the ,rigidity itself. The ideal structure is a porous one, in whicheach little pore forms a completely lsealed cell Within which gas unitscan form during exposure.` These cells-should have negligiblelight-scattering properties, andhence bevery small in relation to thefinal bubble size. In the gelatin type vehicles, the small cellsactually contain water, namely the water of emulsification of thegelatin. This water contains the sensitizer in` solution, whereasprecipitated sensitizer formsk on the cell walls. It is within thesesmall cells that the gas is released and collected during exposure. Inother vehicle types the cells are formed by plastic walls and containonly such gas as is entrapped during the compounding of the vehicle.

The support can be of any suitable material, which will be transparentif the exposure takes place therethrough or the reproduction is intendedto be a diapositive.` Glass, acetate film and'similar substances aresatisfactory, provided they withstand the operational temperaturesrequired. v

.Opaque supports will generally be fiexible such as paper or syntheticsheet material. These supports can be of any desirable color. Dependingon the refiection characteristics of the backing or support, thediffusing bubble record will appear thereon lighter or darker; this mustbe taken into consideration in describing the photographic sign of therecord as will be pointed out below.

Example I 100 g. of high grade dry gelatin such vas sold under thetradedesignation Kodak Peabody Gelatin is soaked for two hours in 1900ml. distilled water of 30 C. To this is added 8 gjcitric acid C.P., andl0 g. of the sensitizing substance sold under the trade designationEdwal Compound #8, which is a zinc salt of para diazo dimethylaniline.This is then diluted to vmake 2000 ml. This emulsion is coated byconventional means on glass plates or cellulose film of the types usedfor purposes of commercial photography, to a thickness of about 2 milsto 0.6 mil., rather, less than more, depending on process controldetails and record requirements. This material, coated on a commercialcellulose film, is for example exposed 4to an original film inconventional contact or projection printing apparatus for copyingmicrofilm, such as a blower cooled standard 35 mm. film projectormodified.

for use as a contact printer with the film stage which consists of -twospring loaded glass rectangles, holding the original film to -be copiedand the film to be exposed in a plane perpendicular to the optical axis.

The exposure time depends upon the output of the exposure flamp in therange of spectral sensitivity of the material (here within a bandbetween about 3000 A. to 4200 A.), upon the density of the original, andupon the efiiciency-of thelight gathering system used. Exposuretimesranging from one second to-several minutes have been successfullyused for the above material.

The -gas is then allowed to diffuse for about 30 minutes 10 plied, inthe manner described above for the developing procedure within thereversible ranges A, B of Figs. 7 and 8.`

Example II The record forming exposure should be of fairly highintensity in View of the facts that most sensitizing substances atdisposal for present purposes are only moderately sensitive,and thatprolonged exposures are not only undesirable from ythe point of view ofshop or ofiice practice but might introduce temperature changes withinthe vehicle which cannot be easily controlled or prevented. It ispossible to utilize an illumination source for heating the copyingmaterial, but the control of such heating complicates the printingsetup. Short time high intensity exposure such as by way of arc lampswith efficient reectors, placed fairly close to the printing material,was

' found to be quite satisfactory, permitting exposure times or less,depending on ythe thickness of the vehicle layer;

5 minutes is the average for thin films. The lm is then relaxed byheating it for a few seconds to about 200 F., between two .metal plateswhich are electrically heated and'thermostatically controlled, or byinfrared radiation. Thisy is a heating within the reversible rangediscussed above with reference to Figs. 7 and 8. An overall exposure isthenlapplied, of an intensity and duration which are about the same asrequired for the above exposure through the original.

1If it is desired to harden the vehicle irreversibly, in region C ofFig. 7, a temperature of about 250 F. is apof a few seconds which orderof magnitude can be easily managed by comparatively unskilled operators.This is important since the prescribed exposure time is fairly closelytied to the properties of original and copying material and should berather carefully adhered to.

Conventional contact or projection printing apparatus can be used forpurposes of the invention. In an installation for copying microfilm, ablower cooled standard 35 mm. film projector has been modified for useas a contact printer. 'I'he projection lens can be used to observe thefilms during exposure. The condenser system efficiently collects theprojector lamp light to channel a maximum proportion thereof through thefilm to be exposed, and to permit the use of smaller light sources. Forother purposes, exposures have been made directly by General ElectricAH-6 mercury are lights, by photoflood lamps,-and by projection lampsalone, in the film stage of microfilm readers. W

The rate of gas diffusion from -the exposed areasyof a particularvehicle sets an upper limit on the length f exposure. Underexposureresults in lack of record, or in thin records of inadequate contrast.Overexposure rresults in fogging at the edges of records due tosensitizer decomposition or bubble expansion beyond the record contours.Unless the sensitive material is purposely exposed in relaxed condition,care must be taken not to have the film so close to the light source asto permit heat to cause relaxation and hence development duringexposure. Forced cooling can be used. f

The emission spectrum of the source of radiation should be chosen with aview to the particularr sensitivity of the' sensitive substance. Apreferred embodiment using Edwal #8 in gelatin asy above described, issensitive to radiation within the wavelength band of 4200 A. down to3000 A.; this permits the use of ordinary orange room light forhandling.

Overall fixing and developing exposures such as will be described beloware less critical. For most fixing purposes overexposure is harmlesssince complete exhaustion of sensitizing substance is desirable.Suitably diffused sources including daylight, are practical for thispurpose. Overall reversal exposures are generally speaking similar tofixing exposures.

Rigiditycontrol of the vehicle for purposes of development aswell asfixation can becarried out in various ways as indicated above, mainly byapplication of heat or moisvrture orboth.

Temperature control is the principal expedient for adjusting rigidityaccording to the invention. It can be effected by way of convection suchas treatment in an oven or air stream, or by conduction such as by wayof heat controlled plates or baths, or by radiation such as infraredrays. Combinations of such temperature control methods are possible andin use.

One practical method of heat treatment is to place the material afterexposure in range A (Figs. 7 and 8) between two metal plates which areelectrically heated and thermostatically controlled within the range of180 F. to 235 F. This has been a thoroughly satisfactory developmentmethod for gelatin type vehicles. A few seconds suflice for developmentin range B, and an additional to 2O seconds lead to range C and fixationthrough irreversible hardening of the vehicle.

For heating gelatin vehicles to range C, irradiation with infraredenergy has also been found satisfactory. It' properly controlled, thisinduces fixation through irreversible hardening of the vehicle andoptical screening.

A method frequently used for developing gelatin vehicles is to combinetemperature and moisture control by passing exposed material rapidlythrough an atmosphere or jet of low pressure steam. The warmth of thesteam cloud or low pressure jet, somewhat below 212 F; and thus withinthe desired temperature range B, together with the moisture serve todevelop out the latent record. It will be understood that theseconveniently adjustable temperature and moisture controls are materiallydependent upon 4initial and thereafter unchangeable selection of otherfactors, such as thickness and inherent porosity and plasticityproperties of the vehicle material.

'Ihe relaxation time required for development is generally not ver]critical; between 2 and 5 seconds suce in most instances forsatisfactory development. For ixation there is no particular time limit.

Several methods for fixation of vehicle and record are practical andwill now be described. As will become apparent from the practicalexamples, they can be used individuallyor combined, according tocircumstances.

Application of hea-t for changing from relaxed condition in range B toindurated condition in range C or A (Figs. 7 and 8) is the principalfixation expedient. This change from relaxed developing to induratednondeveloping condition involves mainly controlled and fairly rapidapplication of heat or quick cooling. The expedients used for changingfrom range A to B can be used such las hot plates, -air blast devicesand heat radiators, and temperature control is -accomplished withconventional thermostats. In the case of gelatin vehicles, satisfactoryxation is accomplished by keeping the material between controlledtemperature hot plates, beyond the required development time. A time of5 to 20 seconds, depending on the temperature gradient, has been foundto be adequate, leading to a great degree of permanence. Anothertechnique is `application of infrared light continued beyond therequired development time.

Gasdilusion is another important fixation expedient. After development,the entire film surface can be exposed to light of intensitysufcient tocause pho-tolysis. if the vehicle is then not placed again indevelopment condition the released gas does not form bubbles butdiffuses out of the film. Sutiicient fixation exposure to destroy allphotosensi-tive material not originally imaged exposed and developed hasbeen `achieved in times generally about the same as required forexposure of the record proper. After such exposure, the diffusionprocess requires from 2 minutes to 30 minutes, the time depending on thethickness ofthe vehicle layer.

Because yof the availability of the diffusion method of fixation, it isnot always necessary to introduce lixation as a definite step in theVprocess. The developed mate-rial if put to routine use is in some casesnecessarily exposed to suicient light to complete photolysis in thepreviously unexposed areas. Thereafter, in ordinary storage, thereleased gas diffuses out and leaves the non-record areas clear andincapable of further change. It will however be understood that fixationaccording to the invention is in many cases an important andindispensable step.

Four different practical embodiments, some of them with optionalvariations will now be described by way of example. Since the underlyingtheoretical considerations and the procedural details which areselectively used in these examples `are su'ciently described above, theywill not now be repeated, unless specic circumstances call for one orthe other detailed directions.

Due to the adaptability of the present system, it is very Y easy, by wayof minor procedural changes, to make copies of the same as well asopposite photographic sign. As herein understood, the term photographicsign describes the general gradation relation of original and copyV sothat any reference herein to printing with the same sign means making apositive from a positive as well as a negative from a negative, andprinting with opposite sign means the making of negatives from positivesas well as of positives from negatives, the term positive and negativebeing used in a relative sense to express mutually complementary recordpatterns, independently of the character of the support which lfor thispurpose is assumed to be transparent.

The `adaptability of the present system is similary advantageous withregard to the fixation procedure which can be easily modified for anypractical purpose.

In Figs. 9 -to 12, only the coatings C are mainly shown, for the sake ofsimplicity. The various phases undergone by Ithe sensitizer areindicated in the same manner as in Figs. 1 to 6. The three vehicleconditions are indicated by single, double 4and triple contours,corresponding to temperature ranges A, B and C respectively.

Fig. 9 shows at a9 an ioriginal O directly superimposed upon a film Fwhich consists of a coating C and a support S. The coating C comprises avehicle v and a sensitizing substance indicated by dots m. The originalO can for example be a microlm and the two elements O and F can beexposed in the above-mentioned modified projector. Assuming that thecoating is of the type described `above in material Example I, thevehicle is at room temperature and hence in indurated conditioncorresponding to range A of Fig. 7. Upon exposure the original Oirnpresses its record upon the beam L of collimated light, establishinga radiation image in terms of sources s. As indicated at b9, thisexposure produces a record pattern composed of units u.

At C9, the vehicle is then relaxed as above described with reference toFig. 7, by raising the temperature into range B. This induces expansionof the gas units u into gas bubbles b. The coating C now contains arecord, corresponding yto the original O, in terms of visible bubblescontaining gas, and unexposed sensitizer mc. In order to xate therecord, various techniques can be ernployed in accordance with theinvention,.as discussed Iabove. Three optional xing procedures will nowbe explained.

As indicated a-t d9, the coating C can be brought into induratedcondition by cooling it to region A which will inhibit expansion of thegas units ud. A uniform exposure is applied and the gas developed duringsuch exposure allowed to diffuse through the vehicle which, it will beremembered, is still permeable. The record defining bubbles b solelyremain as shown at e9 of Fig. 9.

An alternative uses the possibility of hardening the vehicle intemperature region C, as indicated a-t i9 of Fig. 9. This arrests withsafety any further expansion and it is in this case unnecessary to makecertain whether or not an overall ixing exposure is applied and the gaspermitted to diffuse.

A further alternative is shown at g9. In this instance the vehicle isrendered opaque for actinic light as indicated by cross hatching of thediagrammatical showing of layer C. As mentioned above, this technique ofimparting an optical filter action to the vehicle can be connected withthe tanning in accordance wih f9 in which case xation is even more safe,although it will be understood that either procedure f or g issufficient, and that the respective steps can be separately applied bymeans which are expedient in any particular environment.

This modification results in a record of opposite photographic sign fromthat of the original.

As indicated in Fig. 10, the iirst two steps n10 and blO are in thisinstance identical with steps a9 and b9 of Fig. 9. However, `Where-asaccording to Fig. 9 the vehicle is relaxed immediately after exposure inindurated condition, the gas is here given suflicient time to diffusefrom the Vehicle, as indicated at C10. A negative record in terms ofsensitizing substance mc remains. At d10 this is now given an overallexposure that converts the sensitizer molecules into gas units ud. Thevehicle is thereupon relaxed, permitting the gas units to expand andform bubbles be as shown at e10. It will be noted that in this instanceiixation is unnecessary so far as remaining sensitizer is concerned, butfor mechanical reasons another induration can be applied as indicated atf10.

This technique produces a inal record of the same sign as the original.

In the example according to Fig. 11, the iirst two steps are similar toa9 and b9 of Fig. 9, namely exposure and gas unit formation atapproximate room temperature. The step cll is similar to step C10,namely the diiusion of the exposed portions, resulting in a negativerecord in terms of sensitizer molecules mc. The vehicle is thereuponrelaxed and an overall exposure applied which results in a negativerecord in terms of bubbles shown at bd. The vehicle is then indurated orhardened in temperature region A or C, which results in the permanentrecord indicated at ell. It will be noted that this is the techniqueaccording to Example I.

The record ell is of the same photographic sign as the original.

As indicated at a12 of Fig. 12, the vehicle is in this instance inrelaxed condition during exposure. As indicated at b12, the irradiatedsensitizer molecules immediately expand to form bubbles bb, Whereas inthe unexposed portie-ns the sensitizer m is not aiected. As indicated atcl2, an overall exposure is then applied after the Vehicle has beenindurated. This preserves the record in terms of gas bubbles whereas theremainder consists of units. This record can then be iixed in any one ofthe ways described above with reference to Pig. 9. Fig. l2 indicates apreferred embodiment according to which the gas is permitted to diiusefrom condition 14 C12, `which provides an indurated vehicle record interms of empty gas bubbles bf.

The record according to this modification is of opposite sign to theoriginal.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents whichV fall within the scope of the appended claim.

We claim:

A method for producing essentially stable photographic records in termsof substantially purely textural changes of a vehicle whose rigidityvaries reversibly within a given temperature range and which containsdispersed therein a .photolytic compound capable of liberating gas uponirradiation which gas does not eiect said textural changes at a lowtemperature Within said range but eiects such changes at a vehiclerelaxing temperature that is comparatively high within said range,

comprising the steps of exposing said vehicle to record definingirradiation in comparatively rigid condition at a temperature that iscomparatively low within said range, diffusing said gas as liberatedfrom the unchanged vehicle at said low temperature, and subjecting saidvehicle to said high relaxing temperature with application ofessentially uniform irradiation, whereby gas is liberated from thepreviously less irradiated vehicle portions effecting development ofsaid record defining textural changes, thephotolytic compound isessentially eliminated, and the record essentially iixed.

References Cited in the iile of this patent UNITED STATES PATENTS1,571,103 Sury Jan. 26, 1926 1,594,470 Schwarz Aug. 3, 1926 1,919,194Bennett July 25, 1933 1,942,872 Murray Jan. 9, 1934 1,944,293 MartinezJan. 23, 1934 1,952,787 Bennett Mar.` 27, 1934 1,954,325 Martinez Apr.10, 1934 1,990,925 Bennett Feb. l2, 1935 2,018,657 Bennett Oct. 29, 19352,699,392 Herrick et al. Ian. 11, 1955 2,703,756 Herrick et al. Mar. 8,1955 FOREIGN PATENTS 402,737 Great Britain Mar. 4, 1932 898,391 FranceJuly 3, 1944 645,825 Great Britain Nov. 8, 1950

